Recently, optical instruments used in the medical field have been spread. Especially in ophthalmology, optical-characteristics measurement apparatuses for checking eye functions such as the refraction and adjustment of eyes and the insides of eyeballs have been spread. For example, there exists a photorefractometer for obtaining the refractive power and the corneal shape of an eye under measurement.
A retina-image resolution improving apparatus for compensating for wave aberration by deforming a compensation optical member similar to a deformable mirror has been disclosed (for example, in PCT Japanese Translation Patent Publication No. 2001-507258). In this apparatus, laser light reflected from the retina of an eye forms a wavefront on the Hartmann-Shack wavefront sensor through a deformable mirror. The formed wavefront is digitized by a digital processor through a camera to measure wave aberration. The digital-data processor transmits a correction signal to be fed back to the deformable mirror, based on the measured wave aberration. The deformable mirror is deformed to compensate the eye for the wave aberration.